Steam generating unit



p 6, 1966 M. H. KUHNER STEAM GENERATING UNIT Filed April 12, 1965 MAX H. KUHNER 1 NVENTOR tates Patent Ofi Flee 3,270,716 Patented Sept. 6, 1966 This invention relates to a steam generating unit and, more particularly, to apparatus arranged to assure against thermal shock in a steam-and-water drum of a boiler.

As time passes and the designs of steam generating units use higher and higher steam pressures, it is necessary mechanically to reinforce all of the elements of the boiler to withstand such higher pressures. Particularly, this means that the steam-and-water drum wall thickness and the thickness of the downcomer tube wall are increased. Such large metal objects transmit heat rather slowly and are subject to extreme differences in thermal expansion for that reason. The area which suffers most from this effect is the junction between the drum wall and the downcomer tube. When relatively cold feed water is introduced into the bottom of the drum, it sinks to the bottom of the drum, due to the dilference in specific gravity, and comes immediately into contact with the junction between the drum and the downcomer. The elfect of this cold water striking the hot metal surfaces is the efiect called thermal shock. This effect is particularly noticeable at times of rapid change of load where the water level in the drum may drop and the usual body of water may disappear out of the steam-andwater drum altogether, so that the drum and downcomer internal surfaces are exposed. If cold feed water falls on them at that time, cracking and eventual failure may result. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a steam generating unit in which the effect of thermal shock is reduced.

Another object of this invention is the provision of a steam generating unit in which cold feed water is maintained out of contact with the junction between the steam. and-water drum and the downcomer.

A further object of the present invention is the provision of a steam generating unit in which thermal shock, which may take place when rapid lowering of water level in the steam-and-water drum takes place, is .done away with.

It is another object of the instant invention to provide a steam generating unit in which cracking of the steamand-w-ater drum and header and downcomer will not take place, even though relatively cold feed water is introduced into the drum while the water level is such that no hot water exists in the ste'am-and-water drum.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claim appended hereto.

The character of .the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional vie-w of a portion of a steam generating unit embodying the principles of the present invention, and

FIG. 2 is a vertical sectional view of the invention taken on the line IIII of FIG. 1.

Referring to the drawings, the steam generating unit, indicated generally by the reference numeral 10, is shown as consisting of a steam-and-water drum 11 which consists of a long, circular-cylindrical tube having walls of substantial thickness and rounded ends 12. Extending from the top of the drum are steam take-01f connections 13. At one side of the drum are steam release tubes 14 and on the other side steam release tubes 15, the amount of steam released on either side of the drum being substantially equal. From the bottom of the drum extends a plurality of large downcomers 16. In the area where each downcomer 16 joins the wall of the drum 11, it is provided with a thickened portion 17 and, finally, with a fillet 18. The junction between the drum and the downcomer is, therefore, very strong mechanically but, at the same time, is very thick and presents thermal shock problems.

In the lower part of the drum and extending longitudinally thereof is a feed water pipe 19 containing a supply 21 of relatively cold feed water. Underlying the feed water pipe is a tray 22 formed of sheet metal and provided with a fiat, horizontal bottom 23 from the outer edges of which extend inclined sides 24 and 25. The tray is provided with ends 26 located adjacent the ends 12 of the drum, so that the tray is open at the top only and the :feed water pipe resides halfway within the tray 22 with the other half extending above it. Extending from the bottom 23 of the tray is a plurality of sleeves 27, one for each downcomer 16. Each sleeve 27 extends into its downcomer 16 a substantial distance, is concentric with the downcomer, and is spaced from the inner surface thereof to provide an annular space 28 between the inner surface of the downcomer 16 and the outer surface of the sleeve 27. A generally radial plate 29 at one side of the tray and a similar plate 31 at the other side of the tray serve to support it in the lower part of the drum and keep it in spaced relationship with the inner surface of the bottom of the drum.

Overlying the tray 22 and the feed water pipe 19 is a steam separating apparatus 32. A baffle 33 extends upwardly from the plate 31 in front of the lowermost of the steam release tubes 14. A similar bafile 34 resides on the other side of the steam-and-water drum and extends upwardly from the plate 29 in front of the lowermost of the steam release tubes 15. Inwardly of the bafile 33 is a primary separator 35, while a similar separator 36 resides inwardly of the bafile 34. Inwardly of the separator 35 resides a condenser 37, While a similar separator 36 resides inwardly of the baffle 34. Inwardly of the separator 35 resides a condenser 37, while a similar condenser 38 resides inwardly of the separator 36. These condensers are of the type shown and described in the patent of Andrews No. 2,424,212, issued July 22, 1947. To one side of the steam take-01f connections 13 is a drier carton 39, while a similar drier carton 40 resides on the other side of the steam take-01f connections. Underlying the drier carton 40 is a tray 41, while a similar tray 42 underlies the drier carton 39. From the tray 41 extends a drain tube 43 provided with a flared end 44 which resides in the downcomer 16 just below the lower end of the sleeve 27. Similarly, the tray 42 is provided with a downwardly-extending drain tube 45 having a flared end 46 residing adjacent the flared end 44 of the other tube just below the lower end of the sleeve 27 in the downcomer 16. Each of the condensers 37 and 38 are U-shaped tubes, the free end of one leg being attached to the feed water pipe 21 to receive cool feed water 21 and the other leg terminating in the tray 22 for the release of water therein. The condenser tubes are provided with extended-surface elements 47 to provide for optimum heat exchange between the water in the tube and the steam flowing over its outer surface. Finally, in the lower part of the steam-and-water drum resides a body 48 of relatively warm water whose level is normally just above the upper edges of the baflles 33 and 34 so that the lower ends of the primary separators 35 and 36 and of the condensers 37 and 38 reside below the water level.

The operation of the apparatus will now be readily understood in view of the above description. Steam enters the steam-and-water drum through the steam release tubes 14 and 15. Steam from the tubes 14 passes over the primary separator 35 and through the condenser 37, eventually passing upwardly through the drier carton 39 into the steam release connections 13. Similarly, the steam from the steam release tubes passes through the primary separators 36, the condensers 38 and, eventually, flow through the drier carton 40 into the steam take-off connections. Feed water enters the drum through the feed water pipe 19 and passes from there into the condensers 37 and 38. It passes upwardly and then downwardly through the interior of the conden'sers and, eventually, is released into the tray 22. As the steam passes over the condensers 37 and 38, it is condensed and forms a wet stream on the extended surface elements 47 and assists in purifying the steam and removing impurities. The water thus condensed falls into the body 48 of water at the bottom of the drum. The water particles removed from the steam by the drier cartons 38 and 39 flows into the trays 41 and 42 and from there into the tubes 43 and 45, respectively. Eventually, the water originating in the trays 41 and 42 leaves the tubes through the ends 44 and 46 at positions well down in the downcomer tube 16. Most of the water in the body 48 in the steam-and-water drum comes from the waterand-steam mixture discharged from the steam release tubes 14 and 15. This mixture immediately separates and the water in the body 48 flows downwardly around the sides of the baffles 33 and 34 on the outside of the tray 22 and into the annular space between the sleeve 27 and the downcomer 16. Other water from the body flows downwardly into the tray 22 and through the sleeve 27 into the downcomer 16. The relatively cold water originating in the feed water pipe 19 and released from the condensers 37 and 38 flows into the tray 22 and from there flows into the sleeve 27. The bottom end of the sleeve 27 and of the pipes 43 and 45 are well within the downcomer tubes 16 a substantial distance below the junction between the downcomer tubes 16 and the wall of the drum 11. A mixture is formed in the downcomer below the sleeve of the relatively hot water originating in the body 48 and flowing around the outside of the tray, the hot water from the body 48 flowing through the tray, the relatively cool water from the feed water pipe 19 which flows from within the sleeve 27, and the relatively hot water flowing from the ends 44 and 48 originating in the drier carton trays 41 and 42. These fluids are all mixed together due to a substantial ejector action and flow through the downcomer for use in the rest of the boiler. If, on occasion, the load in the unit drops considerably, then the upper level of the body 48 may be lowered in the steam-and-water drum and may, on occasion, even disappear, meaning that the water level may be somewhere down in the downcomer 16. At this time, the cold feed water from the pipe 19 continues to flow into the unit; it flows into the tray 22 and downwardly through the sleeve 27, so that this cold water is kept away from the heavy metal junction between the steam-and-water drum and the drum 19 of the boiler.

The present apparatus is useful in the operation of a steam generating unit in two other respects. It is often necessary in the operation of a unit to shut down the boiler and cool all of the elements as quickly as possible to permit repairs to be made and to allow the unit to be put back on the line as soon as possible. One method, of course, is to run the forced and induced draft fans at full speed to pass cool air through the boiler and to cool the elements that way. However, this is a very slow process. A quicker way is to flood the boiler with cold water. The water, of course, is introduced in the usual way from the feed water pipe and, if this cold water is suddenly brought into contact with the interior of the thick walled steam-and-water drum, considerable damage can take place. By use of the present invention, in such a situation, the cold water flows down the sleeve 27 into the downcomer and the bottom portion of the boiler is filled first. The water, therefore, is heated (in the process of cooling the tubes in the lower part of the boiler) and by the time the water level arrives at the upper part of the boiler where the steam-and-water drum resides, the entire body of water is fairly warm. Therefore, a shock of the interior of the drum is avoided.

Another situation in which the present invention becomes very useful is during ordinary changes of load, when the temperature in the water and the pressure in the drum may drop. At that time, the water passing into the downcomer may contain large bubbles of steam. This inhibits operation of the steam generating unit in two ways. The normal solid body of water in the downcomer promotes nautral circulation, because of the difference in gravity between solid water in the downcomers and steam carrying water in the risers. If, however, steam bubbles occur in the downcomer, the circulation is reduced. Furthermore, the presence of steam bubbles in the Water passing into the downcomer means that the risers and upper parts of the boiler discharge tubes may contain a very high percentage of steam with the consequent possibility of damage to the tubes. By use of the present invention, the cold water from the feed water pipe passes directly into the downcomer and it is thoroughly mixed with the water going into the downcomer. This will cause collapse of any steam bubbles that may exist and avoid the dangers of steam in the downcomer water. There is, therefore, no danger of thermal shock and the connection between the drum and the downcomer will not be damaged, despite the unusual accidental conditions described above.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent A steam generating unit, comprising (a) a steam-and-water drum containing steam-separating apparatus, including a number of steam condensers receiving cold feed water and bringing it into heat exchange relationship with steam,

(b) a feed water pipe extending through the drum in the lower portion thereof and connected to the condensers,

(c) a plurality of downcomers extending from the bottom of the drum,

(d) a tray residing in the lower portion of the drum and spaced from the inner surface of the drum under the discharge end of the condensers, the tray being of substantial capacity to receive cold feed water as it leaves the said ends of the condensers and to prevent it from contacting the drum in the area of its junction with the downcomer and having an upper edge normally above the water level in the drum, from which extends a downwardly extending pipe,

and the lower end of the said pipe extending through (e) a sleeve extending downwardly from the bottom said sleeve a substantial distance into the said downof the tray a substantial distance into each downcorner.

corner concentrically thereof, the said sleeve being 5 spaced from the associated downcomer to form an References Cited y the Examine! annular space between the inner surface of each UNITED STATES PATENTS downcomer and the outer surface of its sleeve, so

that relatively hot water flows from the drum 2,055,781 9/1936 Angermuller 122-459 through the space and mixes with relatively cold 10 7 4 7 1 1 55 Kuhner 122.459 X feed water flowing from the tray and the sleeve, 3,117,560 1/1964 Kuhner 12491 X the mixing taking place in the downcomer a substantial distance from the junction of the dow-ncorner KENNETH SPRAGUE primary Examiner. and the drum, the said steam separating apparatus including a drier carton having an underlying tray 15 FREDERICK MATTESON, Exammer- 

